The MCDB Electron Microscopy Service, located in the Department of Molecular, Cellular and Developmental Biology at the University of Colorado in Boulder, seeks funding to purchase a FEI Tecnai G2 Spirit Bio Twin Transmission Electron Microscope (TEM) from the FEI Company. A new TEM is needed to replace our 23-year-old Philips CM10 TEM, an underperforming microscope that is increasingly difficult to maintain and is currently serving the users of the MCDB EM Service. The FEI G2 Spirit Bio Twin electron microscope is a very versatile 120 KV TEM that is appropriate for most electron microscopy (EM) applications in cellular and molecular microscopy. Its high-contrast lens is well suited to a wide range of specimens and is ideal for low-contrast biological specimens such as negatively stained cellular preparations, high- resolution freeze-fracture replicas and conventional thin plastic sections. The Tecnai G2 Spirit BioTwin is equipped with a computer controlled +/- 70 degree tiltable goniometer stage that can accommodate conventional specimen holders, rotating holders for control of the tilt axis, high- tilt-dual-axis holders for electron tomography(3-dimensional imaging) and state-of-the-art LN2 cryo-holders for imaging vitrified specimens. Seven NIH-funded major users are submitting this application: Dr. Bruce Eaton and Dr. Daniel Feldheim (collaboration on bio-metalic nanoparticles), Dr. Robert Garcea (virus structure and assembly), Dr. Andreas Hoenger (microtubule binding protein structure, technology development), Dr. Leslie Leinwand (myosin mutations and heart disease), Dr. Greg Odorizzi (endosome assembly and structure), Dr. Michael Stowell (membrane protein structure), and Dr. Mark Winey (structure and assembly of MTOCs). The microscope will also service a collection of minor users, both from the University of Colorado and from other institutions. All of the users require the 5-Angstrom point-to-point resolution obtainable with this microscope and the requested Eagle 2K x 2K digital camera system. Many of their projects depend upon the convenient control of the specimen tilt axis provided by this instrument's stage and the requested specimen holders. Altogether, the major and minor users study a wide variety of cell biology topics or molecular structures that are relevant to virology, cancer, heart disease, aging, neurodegenerative diseases, and diagnostic and therapeutic strategies.